Mössbauer Effect in Ferroelectric BaTiO3

Abstract

The Mössbauer effect for ${\mathrm{Fe}}^{57m}$ in the BaTi${\mathrm{O}}_3$ lattice has been studied from 300 to 1200°K with particular emphasis on the region near the Curie temperature. The Mössbauer probe seems to serve as a useful tool for the study of ferroelectrics. The electric-field gradient as seen by the probe at room temperature is -0.52×${10}^{14}$ esu ${\mathrm{cm}}^{-3\mathrm{}}$ and is closely proportional to $P_s^{}{}_{}{}^2$ as the spontaneous polarization $P_s$ varies with temperature. The strength of the resonant absorption was also determined as a function of temperature in the region above $T_c$. Much above $T_c$ these measurements are compatible with a Debye temperature of 450°K. However, as the Curie temperature is approached, the Lamb-Mössbauer factor decreases appreciably. These results are discussed in the light of Cochran's theory of ferroelectricity. From the isomer shift at room temperature (0.50±0.02 mm/sec with respect to 310 stainless steel) the over-all degree of ionicity is estimated to be 60±20%. The temperature shift shows a discontinuity at $T_c$ and is attributed to the change in covalent binding.